Functional proteomics is one of important areas of post-genome researches and this functional proteomics is expected in the future to be broadly used as a key technology for developing a new drug in several fields including protein expression pattern analysis, biomarker analysis for diagnosing disease, search of new biomarker and new drug target, and screening of candidate drugs. However, breakthrough technology for the facilitation of proteomics research is needed, and this technology is thought to be highly sensitive protein microarray chip technology. Protein chip technology is for a large amount of and concurrent analysis using reaction of chip surface on which biomolecules such as protein, antibody, peptide, ligand and so on are micro-arrayed densely, and is being rapidly developed with DNA chip according to an introduction of the importance of protein interaction and functional analysis caused by human genome map project.
Integrin receptor is cell surface receptor controlling important physiological activities of cell such as cell adhesion and migration, differentiation, proliferation and so on. Integrin works as heterodimer made by the non-covalent binding of alpha and beta subunit, and alpha and beta subunit, as pairs, constitute 22 kind of integrin family. That is, this ligand specificity is different from each kind of integrin and one kind of integrin can be bound with several ligands at the same time. The kind of ligand is really various and mainly extracellular matrix proteins (vitronectin, fibronectin, collagen, laminin, vWF, fibrinogen and so on). Integrin consists of long extracellular domain and short cytoplasmic domain, and the extracellular domain has the motif binding with ligand. Cytoplasmic domain is connected with cytoskeleton in cytoplasm, and the activation of integrin causes cytoskeleton rearrangement and forms focal adhesion complex, with which cell adhesion and migration process are performed. An antagonistic material of integrin αvβ3, for example, is one of disintegrin family derived from snake venom. About 30 materials are known as disintegrin and have a same integral-binding motif, Arg-Gly-Asp (RGD) sequence, and have an ability inhibiting the binding of integrin and ligand. These block α11bβ3 integrin, one of integrins present on a platelet surface and inhibit the binding of ligand fibrinogen, which suppresses platelet aggregation. Because of this characteristics of disintegrin, the disintegrin works as an antagonistic material of integrin αvβ3 and thus suppresses angiogenesis.
Phase 1 clinical trial of Vitaxin, a humanized mAb against integrin αvβ3, for treating solid tumor has been successfully established without any severe toxicity and Phase 2 clinical trial is being performed now. An interesting fact is that the cancer tissue of one patient among 12 patients of clinical trial decreased by over 50%. EMD121974 developed by Merck company is a small molecule (cyclic RGD peptide) inhibiting endothelial integrin αvβ3, and its phase 1 clinical trial is being done. This material is a cyclic pentapeptide having RGD sequence and is shown through animal test to have an activity inhibiting angiogenesis and thus suppressing cancer growth in human malignant melanoma and so on. Mechanism of endostatin has not been understood for a long time, but recently recombinant human endostatin is established to interact with blood endothelial alpha(5) and alpha(v)-integrin and thus inhibit integrin-dependent endothelial function such as endothelial cell migration. Therefore, these results demonstrate that it is possible to develop an antagonistic material of integrin as angiogenesis inhibitor for treating cancer.
Technology used until now for searching antagonistic material of integrin is Enzyme Linked Immuno Sorbent Assay (ELISA), one of technologies broadly used for diagnosis in research center or hospital. However, this method is not appropriate for large screening because it needs a large amount of protein and is non-specific.